Add a simple utility to detect profiling bias.

test/analyze/prof_bias.c

@@ -0,0 +1,60 @@
+#include "test/jemalloc_test.h"
+
+/*
+ * This is a helper utility, only meant to be run manually (and, for example,
+ * doesn't check for failures, try to skip execution in non-prof modes, etc.).
+ * It runs, allocates objects of two different sizes from the same stack trace,
+ * and exits.
+ *
+ * The idea is that some human operator will run it like:
+ *     MALLOC_CONF="prof:true,prof_final:true" test/analyze/prof_bias
+ * and manually inspect the results.
+ *
+ * The results should be:
+ * jeprof --text test/analyze/prof_bias --inuse_space jeprof.<pid>.0.f.heap:
+ * 	around 1024 MB
+ * jeprof --text test/analyze/prof_bias --inuse_objects jeprof.<pid>.0.f.heap:
+ * 	around 33554448 = 16 + 32 * 1024 * 1024
+ *
+ * And, if prof_accum is on:
+ * jeprof --text test/analyze/prof_bias --alloc_space jeprof.<pid>.0.f.heap:
+ *     around 2048 MB
+ * jeprof --text test/analyze/prof_bias --alloc_objects jeprof.<pid>.0.f.heap:
+ * 	around 67108896 = 2 * (16 + 32 * 1024 * 1024)
+ */
+
+static void
+mock_backtrace(prof_bt_t *bt) {
+	bt->len = 4;
+	bt->vec[0] = (void *)0x111;
+	bt->vec[1] = (void *)0x222;
+	bt->vec[2] = (void *)0x333;
+	bt->vec[3] = (void *)0x444;
+}
+
+static void
+do_allocs(size_t sz, size_t cnt, bool do_frees) {
+	for (size_t i = 0; i < cnt; i++) {
+		void *ptr = mallocx(sz, 0);
+		assert_ptr_not_null(ptr, "Unexpected mallocx failure");
+		if (do_frees) {
+			dallocx(ptr, 0);
+		}
+	}
+}
+
+int
+main(void) {
+	size_t lg_prof_sample = 19;
+	int err = mallctl("prof.reset", NULL, NULL, (void *)&lg_prof_sample,
+	    sizeof(lg_prof_sample));
+	assert(err == 0);
+
+	prof_backtrace_hook = &mock_backtrace;
+	do_allocs(16, 32 * 1024 * 1024, /* do_frees */ true);
+	do_allocs(32 * 1024* 1024, 16, /* do_frees */ true);
+	do_allocs(16, 32 * 1024 * 1024, /* do_frees */ false);
+	do_allocs(32 * 1024* 1024, 16, /* do_frees */ false);
+
+	return 0;
+}